Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $238.62   6.153%   $253.3023   $253.30   $253.30   $253.30  
  Purchase #2 $142.53   5.494%   $150.3606   $150.36   $150.35   $150.40  
  Purchase #3 $171.89   9.482%   $188.1886   $188.19   $188.20   $188.20  
  Purchase #4 $44.69   5.636%   $47.2087   $47.21   $47.20   $47.20  
  Purchase #5 $249.37   4.254%   $259.9782   $259.98   $260.00   $260.00  
  Purchase #6 $64.79   5.365%   $68.266   $68.27   $68.25   $68.30  
  Purchase #7 $75.87   9.607%   $83.1588   $83.16   $83.15   $83.20  
  7 purchase totals = $987.76       $1,050.4632   $1,050.47   $1,050.45   $1,050.60